White patches on cactus likely mealy bugs

MRT

Published 11:31 am, Tuesday, November 13, 2012

Dear Neil: I have a medium-sized cactus I've had on my patio since 2007. In the middle of this past summer, it began developing little white patches on a couple of its leaves. The patches look like small shredded Styrofoam, and they have spread to the entire plant. I've used a houseplant insecticide, but with no results. What are they, and what can I do?

Answer: It sounds like your plant has a dose of mealy bugs. (You can confirm that by looking up "photo mealy bugs" online.) They're a particularly obnoxious type of soft-bodied scale insect, and you're going to have to be very persistant to get rid of them. Systemic insecticides offer good help. Local retail garden centers will be able to show you several. (They're not commonly sold in national chain retailers.) You can also use a cotton swab dipped in rubbing alcohol to remove them physically. While it's boring and tedious, it's very effective. If you see them showing up on other plants, address them immediately.

Dear Neil: How much cold can Gold Star esperanza tolerate? When, and by how much, can I prune mine? They have started to get rather leggy.

Answer: Gold Star esperanzas are winter-hardy in the southern half of Texas, but they'll survive farther north in mild winters, and they'll be killed in South Texas in severe winters, so it's all relative. It's best to grow them in protected locations (against the house, in alcoves, atriums, etc.). Pruning should be done as needed, rather than a large amount at any one time. However, if you do need to do major pruning, late winter would be the best time, so you can take full advantage of the flush of spring growth. If your plants are getting lanky, be sure they're getting full, or nearly full sunlight.

Dear Neil: Now that my red oak leaves are falling, I'm seeing tons of what look like bright red acorns (along with the regular acorns). They seem to have been stuck to the leaves. What are they, and do I need to worry about them for next year?

Answer: Those are insect galls. There have been tons of reports of them this year (more than most years). The adult female insect stings the plant's leaf or twig and inserts eggs. The red growth you see is all plant tissue that forms as a response to the sting. The insect's larvae are developing within the swollen area. There is no effective spray for them, but that really isn't critical, because they really don't do any measureable harm to their host trees. You'll see hundreds of different types of galls on oaks alone, and they're common on hackberries, cottonwoods, pecans and other shade trees. No cause for concern.

Dear Neil: I've tried your suggestion of hand-digging my briars, and it has worked. It wasn't much trouble, either. However, now I'm faced with getting rid of trumpet vine. Is there any way short of digging it? You know how it spreads everywhere.

Answer: If the mother plant still exists, and if you want to save it, begin by putting a root barrier around it. Dig a trench 20 inches deep four or five feet away from its trunk and insert a heavy vinyl pond liner. Use a broadleafed weedkiller spray on the sprouts as they begin to grow actively in the spring. If you want to eliminate the entire planting, cut the mother plant off at the ground. Leave its stump in place. In early spring, just before new buds sprout, drill into the stump with a quarter-inch bit to make a "reservoir" for the herbicide, then pour the same type of broadleafed weedkiller in at full strength. You'll still have to spray some of the rootsprouts as they continue to grow, but you'll generally be able to kill the mother plant out with one treatment.

Dear Neil: When I bring tropical plants into the house for the winter, most of their leaves fall off. Is there any good way to prevent that?

Answer: That's caused by a change in the lighting. The plants have become acclimated to outdoor conditions. When they're suddenly thrust into darker spots, the leaves respond by yellowing and dropping. All the fertilizer and water you might add won't make any difference. It's a lack of light, pure and simple. Make the changes gradually, and try to give them the same amount of daylight they were receiving outdoors.